This invention relates to a distributor type fuel injection pump used in an internal combustion engine, and more specifically, to a distributor type fuel injection pump adapted to attenuate noise attributed to combustion sound produced in an internal combustion engine when the engine is in low-speed rotation or in low-load operation.
When in low-speed rotation or in low-load operation, e.g., when idling, a diesel engine, for example, suffers higher noise attributed to combustion sound than does a gasoline engine. As a measure to counter the noise of the diesel engine, a method is conventionally known in which the injection rate (injection quantity per unit time) of fuel injected into the combustion chambers of the engine is lowered when the engine is in low-speed rotation or in low-load operation. This method is applied to distributor type fuel injection pumps stated in Japanese Utility Model Disclosure No. 105656/81 and Japanese Patent Disclosure No. 154158/81.
In the fuel injection pump stated in Japanese Utility Model Disclosure No. 105656/81, however, the amount of fuel injected is reduced too much to keep proper operation of the engine in low-speed rotation or in low-load operation, so that the fuel injection quantity is substantially reduced.
In the fuel injection pump stated in Japanese Patent Disclosure No. 154158/81, on the other hand, the amount of fuel to be injected varies solely depending upon the variation of the inner diameter of the return or accumulation passage, and moreover the time of fuel injection is retarded, since it takes no measure to control pressure at the entrance to the return or accumulation passage. Thus, the injection rate cannot be controlled with a high degree of accuracy.